Electrochemical characterization and physically based modeling of lithium-ion batteries

This work aims at the developing of a battery model, which simulates the operating voltage U-op of a high power lithium-ion battery at varying operating conditions. U-op results from the open circuit voltage U-ocv and the sum of overvoltages eta(I) that exist when the battery is under load: U-op = U-ocv (T, SOC) + eta(0) (T, SOC,I) + eta(CT,C) (T, SOC, I) + eta(CT/SEI,A) (T, SOC, I) + eta(Diff,A/C) (T, SOC, I) The open circuit voltage U-ocv is determined with a quasi-stationary method. The ohmic loss eta(0) and the interface losses eta(CT.C) and eta(CT/SEI,A) are measured and separated by the application of electrochemical impedance spectroscopy measurements in the high and middle frequency range and a corresponding DRT-analysis. Using an equivalent model (ECM) enables the quantification of those loss processes and provides their resistance and time constant which are required to calculate the overvoltage. The lithium solid state diffusion losses eta(Diff,A/C) are studied by a current interruption method in the time domain which is the method of choice in the low frequency range and which equally provides the resistance and the time constant of the process. Finally, a continuous discharge curve is simulated. The ECM also serves as a basis for physically motivated fractional identification methods which estimate the impedance parameters out of time domain data. These methods, in turn, can be used for online parametrization of the presented battery model.